This invention relates to the formation of deposits inhibiting fluid flow in conduits and the like, and more particularly relates to methods and means for preventing the formation of deposits and the like in downhole pipe and other conduit environments, using magnetic fields generated by in situ permanent magnets.
It is well known in the prior art that paraffin, asphaltene and salts dissolved in water are important constituents of most crude oils. It is also well known that these constituents tend to form deposits in pipelines located oil field and refining operations, which inhibit fluid flow and thereby adversely affect production throughout the oil industry.
As will be appreciated by those skilled in the art, the nature and content of such adverse deposits vary as a function of various parameters including crude oil rheological composition, formation temperature, well depth, pressure drop, and even method of production.
Paraffins comprise straight-chains or branched alkanes of relative high molecule, weight. Asphaltenes comprise dark brown to black components present in crude oil with a relatively high molecular weight. J. G. Speight and S. E. Moschopedis, in their paper "On the Molecular Nature of Petroleum Asphaltenes," published in Am. Chem. Soc. Proc., 1981, report that there are indications that asphaltenes consist of condensed aromatic nuclei that carry alkyl and alicyclic systems with heterocyclic elements, i.e., nitrogen, oxygen, sulfur, scattered throughout. Studies of the elemental compositions of asphaltene fractions precipitated by different solvents indicate that the amounts of carbon and hydrogen present in deposits usually vary over only a narrow range, e.g., 82+3% carbon; 8.1+0.7% hydrogen. J. G. Speight, "The Structure of Petroleum Asphaltenes," Inform. Series, Alberta Research Council, No. 81, 1978 and 178th National Meeting, Am. Chem. Soc., Washington, D.C., Sept. 1979.
Nevertheless, earlier research found that variations occur in the proportion of the heterocyclic elements found in asphaltene deposits, particularly oxygen and sulfur. Nitrogen content, on the other hand, seems to remain relatively constant. P. A. Witherspoon and Z. A. Minir theorized, in the paper entitled "Size and Shape of Asphaltic Particles in Petroleum" delivered at the AIME Fall Meeting, Los Angeles, Calif., Oct. 1958, that asphaltenes are located in the nucleus of an immense collection of molecules called "micelies." Surrounding this nucleus are lighter and less aromatic constituents that resemble alkanes found in paraffins called "resins." Thus, it believed that based upon observations of this structure that asphaltene particles form and behave like colloids.
It is well known in the prior art that colloidal particles remain suspended so long as equilibrium between the particulate phase and the solvent phase is maintained. If, however, equilibrium conditions change even slightly, paraffin may precipitate from the crude oil solvent phase. It was reported by C. E. Reisle, in his paper, "Paraffin and Congealing Oil Problems," Bull. USBM, p. 348, 1932, that the most significant cause of this precipitation is decrease in temperature. It will be appreciated by those skilled in the art that paraffin molecules, even in crystalline form, tend to remain colloidally dispersed in crude oil, unless the paraffin molecules are caused to congeal by nucleating materials. Such nucleating materials act as catalysts to accumulate paraffin molecules and crystals into agglomerations much larger in dimension than paraffin single crystal formations. These agglomerations ultimately can no longer remain colloidally dispersed in crude oil and precipitate out, thereby forming deposits throughout the well's producing system and concomitant equipment, both downhole and at the surface. The nucleating materials in the crude oil colloidal suspension include asphaltenes, corrosion products, salts dissolved in water and formation fines. As is known in the art, all of these nucleating materials carry an electrical charge.
In the case of asphaltene, the transfer of peptizing agents, i.e., resins, from the asphaltene phase to the crude oil phase and vice-versa is responsible for the aggregation of asphaltene micelies and their flocculation into larger entities which causes precipitation out of colloidal suspension. Since the highly polar centers of the asphaltene micelies have a natural tendency to attract each other and thereby aggregate and flocculate, and, of course, as a result, no longer remain suspended throughout the crude oil phase.
Similarly, it is also well known in the prior art that scale deposits frequently form when natural water flows through pipes and other thermodynmnic vessels. Such natural water contains various dissolved or suspended minerals which can be caused to precipitate out and form scales and the like. The scales usually consist of solid deposits comprising precipitation salts, like barium sulfate, calcium sulfate, magnesium sulfate, magnesium carbonate, calcium carbonate, etc.
It is common knowledge that paraffin, asphaltene and scale deposits typically vary from one reservoir to another. Indeed, sometimes differences in deposits have even been observed in wells in the same reservoir. Them have been many attempts in the prior art to provide means and methods for minimizing the adverse affects of deposit formation on fluid flow in downhole and surface oil operations and water flow systems. Such attempts to improve this art teach a variety of mechanical, chemical, thermal and magnetical systems for removing paraffin, asphaltene and scales, or for preventing this deposit-fonnation process.
For example, in U.S. Pat. No. 5,178,757, Corney teaches a magnetic tool for conditioning fluids which includes a hollow core providing at least one passage through which the fluid to be treated flows. An array of magnets extends longitudinally along the core with the poles of the magnets arranged to provide a magnetic field perpendicular to the flow path to enhance the magnetic conditioning effect of the tool. But, unfortunately, there is only a limited exposure of the charged particles in the colloidal suspension to the magnetic field: the short straight linear path taken by the charged particles affords minimal exposure to the magnetic lines of force.
As another example, O'Meara, in U.S. Pat. No. 4,564,448, discloses a magnetic fluid treatment tool comprising a hollow, cylindrical housing containing a central magnetic assembly and one or more concentric ring magnetic assemblies. Another passageway between the core magnet assembly and the ring magnet provide fluid flow paths through the O'Meara tool. Since O'Meara teaches magnets directly in contact with liquid flowing through a conduit, its applicability is restricted to aqueous liquids and the like. Viscous and heterogeneous fluids like crude oil would foul the in situ magnets and interfere with the operation of this tool. Furthermore, the magnetic field is perpendicular to the flowing aqueous fluid only in four locations, i.e., at the four concentric ring magnets. Accordingly, the magnetic flux is closing not through the flowing fluid, but through the other elongated magnets.
Another contribution to the art was made by Debney et al. wherein in U.S. Pat. No. 4,422,934 is disclosed a magnetic device for the treatment of calcareous fluids. This device has an elongate housing with an inlet and an outlet for the flow of liquid therethrough. The magnets are held in position by a plurality of transverse holding elements which are positioned so that the magnets are angularly disposed in a helical arrangement. The magnets are directly immersed in the fluid flowing through the device. Unfortunately, the magnetic flux is almost parallel to the flowing fluid. Thus, the affect of the magnetic field on the charged particles scattered throughout the fluid will be weak.
A recent improvement in the prior art is taught by Harms et al. in U.S. Pat. No. 5,042,491 with regard to a method and tool for controlling paraffin deposits in oil flow lines and downhole strings. The Harms approach is to interrupt the flow of electrostatic forces by functioning as a static drain, removing the affects of frictional static forces built up during oil flowing in pipelines. The presence of a nonmagnetic and nonconductive liner provides a magnetic shield which theoretically interrupts this electrostatic flow. Again, the Harms invention suffers from the inherent deficiency of providing only a minimal exposure of the charged particles to the influence of the magnetic field.
Similarly, other prior art magnetic tools have consisted of little more than means for suspending magnets around a piping system through which flowing fluid passes. Examples of this form of magnetic fluid conditioning tools are generally described in U.S. Pat. Nos. 4,299,700; 4,417,984; 4,455,229; 4,422,935; 4,289,621; 4,278,549; and 3,228,878; and in Japanese Patent No. 189,991; United Kingdom Patent Nos. 1,311,794 and 2,023,116; Soviet Patent No. 590,438; French Patent No. 2,236,788; and German Patent No. 1,642,524.
While, as hereinbefore exemplified, practitioners in the art have attempted to improve the means for removing deposits from pipelines and the like, there has been less effort expended to prevent the formation of such deposition. But, with the demands for increased oil production from limited natural resources, even relatively small increases in the exposure of charged asphaltene colloidal particles in crude oil to the affects of magnetic fields have been found to significantly improve the stability of colloidal suspensions, thereby minimizing and even preventing depositions on pipelines and the like.
Similarly, minimizing or preventing scaling in water systems and even minimizing or preventing deposits in the vascular systems in humans may be achieved if the colloidal nature of flowing fluids is understood and the suspended particles sufficiently stabilized.
Accordingly, these limitations and disadvantages of the prior art are overcome with the present invention, and improved means and techniques are provided which are useful for sustaining the stability of colloidal suspensions in crude oil and the like, and for minimizing or even preventing deposits in pipelines and the like.